A method is proposed for nucleic acid-based diagnostics in vitro. The method employs light-inducible transponders, i.e. miniature transmitter- receivers, activated by laser light for transmission of data. The transponder carriers an oligonucleotide probe, the sequence of which is stored in the electronic memory of the transponder. To determine the presence of the target DNA, the fluorophore-labeled target DNA is hybridized to the oligonucleotide immobilized on transponders. The transponders are then analyzed by measuring the fluorescence originating from the label on the surface of the transponder, and by electronically decoding the sequence of the probe stored on the transponder. The DNA analysis can involve a series of elementary observations, each observation corresponding to a transponder carrying a different oligonucleotide probe. The proof-of-principle will be provided by manufacturing a transponder and experimentally testing the two modes of its action (fluorescence and decoding of the memory) on a modified laser scanning cytometer. The proposal will lead to a new line of diagnostic instrumentation, diagnostic assays, and to the generation of a large amount of nucleic acid-based data relevant for diagnostics in vitro and population studies. PROPOSED COMMERCIAL APPLICATION Commercial applications include nucleic acid based in vitro diagnostics for infectious diseases, cancer, genetic testing, forensic testing, fertility testing, or in vitro fertilization. The successful implementation of the proposal will lead to the development of a new line of instrumentation for diagnostics in vitro.